Survivors provide new information about the 2004 tsunami disaster

It has been nearly five years since the tsunami hit the Indian Ocean on December 26, 2004. Together with survivors of the tsunami disaster, Johanna Mård Karlsson and research colleagues at Stockholm University have built a detailed reconstruction of the coastal impact of the tsunami in the Khao Lak area, Thailand. Besides achieving a better understanding of the event, they have been able to use the reconstruction to verify a new computer simulation of the impact of the tsunami in southeastern Thailand.

The study, based on Johanna Mård Karlsson's master's thesis, was initiated by Michael Sandén, a survivor of the tsunami disaster, who, together with other survivors, hopes that their experiences can be used to limit the effects of future tsunamis and save lives. With their eyewitness accounts and the assistance of amateur videos and a unique photo database as well as on-site field measurements in Thailand, it has been possible to create a holistic picture of the of the coastal impact of the 2004 tsunami in Khao Lak in the form of a reconstruction.

The reconstruction shows that the tsunami hit the Khao Lak tourist area from the west at a velocity of 33 km/h and that the first of at least two waves, with a wave period of 40 minutes, measured 5 meters above ground and reached a maximum distance of about 1.5 km inland. The reconstruction has also been able to show that the incoming wave had a steep profile, which explains the total devastation that was caused by the tsunami impact. A small wave preceded the first main wave, and these two then converged into a wave outside the beaches at Bang Niang and Nang Thong, which explains why these areas of Khao Lak suffered the greatest destruction and larger wave heights.

"With this unique reconstruction, we have been able to verify a new computer simulation that shows how the dynamics of the tsunami affected the critical coastal zones in southeastern Thailand. The computer simulation was done by our research colleagues in Thailand," says Johanna Mård Karlsson. "This represents an important step forward, as improved computer simulation tools can calculate more efficiently and rapidly how a tsunami will impact a coastal area, so we can send out warnings."

With this study the research team has enhanced our understanding of the event and at the same time highlighted the importance of eyewitness accounts as a reliable source when verifying computer simulations. This, in turn, can be used to predict and thereby help prevent similar consequences of future tsunamis.

The study has been published in Journal of Geophysical Research – Oceans.

Note: The 2004 tsunami caused widespread devastation around the Indian Ocean, killing nearly 300,000 people in 12 countries.